The present invention relates to an elongated cutting insert for application in rotary end mills for machining of metallic workpieces. In particular the invention relates to a cutting insert for end mills in order to be able to machine a 90-degree shoulder with greater precision.
The development of milling inserts for end mills generally manufactured through form-pressing and sintering of a cutting material-forming powder is concentrated today on positive cutting edges having positive rake angles since these have showed the ability to reduce the cutting forces and the power supply needed in a tooling machine while at the same time diminishing undesirable vibrations. It is often aimed to provide the tool with a geometry having a positive axial angle and simultaneously a negative radial angle. In certain cases also a combination of positive axial angle and zero degree radial angle can be used in order to obtain a helical chip that provides the best chip transport. The cutting insert is usually clamped with a center locking screw in order to provide the best possibilities for chip transport without problems.
One of the drawbacks with existing usual indexible inserts for end mills has been that they do not enable, with desired exactitude, the machining of a 90-degree shoulder of a workpiece. The problem with this type of machining is that the workpiece wall does not become wholly straight. As a solution to this problem it has been proposed to use a cutting insert, the cutting edges of which are spirally curved. EP-A-416 901 shows and describes such a tool. With such spiral cutting edges the cutting edge can more easily come into engagement with the workplace with an inclined curve of the cutting force up to a maximum value which lies under that achieved with a straight cutting edge. The tool has in this way obtained a somewhat better stability at the same time as the tendency of tool vibrations has been somewhat diminished.
In view hereof it is a purpose with the invention to achieve a modified cutting insert of the type described in EP-A-416 901, with improved geometrical optimization, implying constant functional edge angle in combination with step clearance along a wave-shaped edge line intended to be mounted with large axial inclination in the tool.
It is another purpose to achieve a milling tool, which is useful both for machining of a 90-degree shoulder and for axial machining (so-called ramping), i.e. a tool which machines the workpiece in both axial and radial directions.